NAME

       SSL_set_num_tickets, SSL_get_num_tickets, SSL_CTX_set_num_tickets,
       SSL_CTX_get_num_tickets, SSL_new_session_ticket - control the number of TLSv1.3 session
       tickets that are issued

SYNOPSIS

        #include <openssl/ssl.h>

        int SSL_set_num_tickets(SSL *s, size_t num_tickets);
        size_t SSL_get_num_tickets(const SSL *s);
        int SSL_CTX_set_num_tickets(SSL_CTX *ctx, size_t num_tickets);
        size_t SSL_CTX_get_num_tickets(const SSL_CTX *ctx);
        int SSL_new_session_ticket(SSL *s);

DESCRIPTION

       SSL_CTX_set_num_tickets() and SSL_set_num_tickets() can be called for a server application
       and set the number of TLSv1.3 session tickets that will be sent to the client after a full
       handshake. Set the desired value (which could be 0) in the num_tickets argument. Typically
       these functions should be called before the start of the handshake.

       The default number of tickets is 2. Following a resumption the number of tickets issued
       will never be more than 1 regardless of the value set via SSL_set_num_tickets() or
       SSL_CTX_set_num_tickets(). If num_tickets is set to 0 then no tickets will be issued for
       either a normal connection or a resumption.

       Tickets are also issued on receipt of a post-handshake certificate from the client
       following a request by the server using SSL_verify_client_post_handshake(3). These new
       tickets will be associated with the updated client identity (i.e. including their
       certificate and verification status). The number of tickets issued will normally be the
       same as was used for the initial handshake. If the initial handshake was a full handshake
       then SSL_set_num_tickets() can be called again prior to calling
       SSL_verify_client_post_handshake() to update the number of tickets that will be sent.

       To issue tickets after other events (such as application-layer changes),
       SSL_new_session_ticket() is used by a server application to request that a new ticket be
       sent when it is safe to do so.  New tickets are only allowed to be sent in this manner
       after the initial handshake has completed, and only for TLS 1.3 connections.  By default,
       the ticket generation and transmission are delayed until the server is starting a new
       write operation, so that it is bundled with other application data being written and
       properly aligned to a record boundary.  If the connection was at a record boundary when
       SSL_new_session_ticket() was called, the ticket can be sent immediately (without waiting
       for the next application write) by calling SSL_do_handshake().  SSL_new_session_ticket()
       can be called more than once to request additional tickets be sent; all such requests are
       queued and written together when it is safe to do so and triggered by SSL_write() or
       SSL_do_handshake().  Note that a successful return from SSL_new_session_ticket() indicates
       only that the request to send a ticket was processed, not that the ticket itself was sent.
       To be notified when the ticket itself is sent, a new-session callback can be registered
       with SSL_CTX_sess_set_new_cb(3) that will be invoked as the ticket or tickets are
       generated.

       SSL_CTX_get_num_tickets() and SSL_get_num_tickets() return the number of tickets set by a
       previous call to SSL_CTX_set_num_tickets() or SSL_set_num_tickets(), or 2 if no such call
       has been made.

RETURN VALUES

       SSL_CTX_set_num_tickets(), SSL_set_num_tickets(), and SSL_new_session_ticket() return 1 on
       success or 0 on failure.

       SSL_CTX_get_num_tickets() and SSL_get_num_tickets() return the number of tickets that have
       been previously set.

SEE ALSO

       ssl(7)

HISTORY

       SSL_new_session_ticket() was added in OpenSSL 3.0.0.  SSL_set_num_tickets(),
       SSL_get_num_tickets(), SSL_CTX_set_num_tickets(), and SSL_CTX_get_num_tickets() were added
       in OpenSSL 1.1.1.

COPYRIGHT

       Copyright 2018-2021 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the Apache License 2.0 (the "License").  You may not use this file except
       in compliance with the License.  You can obtain a copy in the file LICENSE in the source
       distribution or at <https://www.openssl.org/source/license.html>.